Bromoacylurethans as antifoggants



United States PatentO 3,232,762 BROMOACYLURETHANS AS AN'IIFOGGANTS John-A. Ford, Jr., and Charles V. Wilson, Rochester,

N.Y., assiguors to Eastman Kodak Company, Rochester, N.Y., a corporationof New Jersey No Drawing Filed July 3, 1963, Ser. No. 292,762 13 Claims.(Cl. 96109) 1 This invention relates to fog-inhibiting agents forphotographic emulsions and to photographic emulsions containing them.

It is well known that photographic emulsions on storage" tend to losesensitivity and to becomespontaneously developable without exposure tolight. There is normally' a detectable amountof the silver salt reducedduring development in the areas where no exposure was given;' this iscommonly c'alledfog, and sometimes called chemical fog Where it isnecessary to distinguish between it and the efiects of accidentalexposure to radiation; in this invention we are not concerned with thelatter.

Fog depends both on the emulsion and the conditions of development; fora given emulsion it increases with the degree of development. Withconstant development conditions, it tends to increase with time,temperature and relative-humidity of storage conditions; it is commonpractice to make accelerated tests of the stability of photographicemulsions by storage atincreased temperature or humidity, or both. Itis, of course, desirable to have emulsions as stable as possible underthe conditions of high temperature and humidity which may occur intropical climates, for example. Fog usually appears over the whole areaof the sensitive coating, but when severe, it is frequently non-uniform.Fog may also be caused by exposure to chemicals, for example,hydrogen'sulfide and other reactive sulfur compounds, hydrogen peroxidevapor, and strongly reducing materials. While antifoggants may protect,to some extent, against such effects, it is normally understood that anantifoggant protects against spontaneous growth of fog during prolongedstorage or storage at high temperatures and humidities, or duringdevelopment to maximum contrast and speed, or both.

It is, accordingly, an object of our invention to provide a new methodfor stabilizing photographic silver halide emulsions.

A- further object is to provide novel photographic silver halideemulsions containing antifoggants or stabilizers.

It is another object of our invention to provide novel photographicsilver halide emulsions that are stabilized with antifoggant addendathat do not objectionably desensitize the emulsions.

Other objects will become apparent from a consideration of the followingdescription and examples.

According to our invention, photographic silver halide emulsions arestabilized with an alkyl bromoacylurethan. These compounds can berepresented by the following general formula:

where n has a value of 1 to 7 inclusive, and R represents a memberselected from the group consisting. of an alkyl radical such as ethyl,butyl, octyl, etc. and a haloalkyl radical such as bromoethyl.

It has also been found in certain instances that a number of thecompounds embraced by Formula I above serve to increase the sensitivityof photographic silver halide emulsions, in addition to stabilizing theemulsions or providing an anti-foggant effect. However, the

'25, 279281 (1960). isomerizing N-bromosuccinimide to 3-bromopropionyl3,232,762 Patented Feb. 1,1966

fog-inhibiting effect is more general than the sensitizing efiect,andfor this reason, these compounds are referred tobelow as antifoggants orfog-inhibitors.

The fog-inhibitors of our invention can be added to the emulsion duringthe process of manufacture, either during mixing, ripening, orafter-ripening, in order to avoid loss of sensitivity and/ or to inhibitthe growth of fog with the passage of time under non-ideal conditions ofstorage.

A solution of the compounds of the invention when added in suitableconcentration, before coating, to unsensitized, chemically sensitized,or optically sensitized photographic emulsions may not appreciablyafiect the sensitometric values for sensitivity and fog whenmeasurements are made soon after coating. Sensitometricmeasurements madeat appreciable intervals of time, at elevated temperatures and-dry orsomewhat humid conditions show that these compounds do stabilizephotographic speed and maintain fog at a low level.

The preparation of silver halide emulsions involves three separateoperations: (1) the emulsification and digestion or ripening of thesilverhalide, (2) the freeing of theemu-lsion from excess soluble salts,usually by washing, and (3) the second digestion or after-ripening toobtain'increased' sensitivity. (Mees, The Theory of the PhotographicProcess (1952).) We prefer to add the fog-inhibiting agents after thefinal digestion or afterripening, although they-can advantageously beadded prior to digestion. If desired, the fog-inhibiting agents of ourinvention can be-incorporated in the emulsions without adverse effectsby the bathing techniques known to those skilled in the art.

Listed below are a number of compounds coming within the-scope ofFormula I above which are typical of the antifoggants of our invention.

Butyl 3-bromopropionylurethan Octadecyl-3-bromopropionyluretl1an Many ofthe compounds embraced by Formula I ....above..have been previouslydescribed in the prior art.

These compounds can be prepared according to the procedure described byJohnson et al. in J. Org. Chem., This method, briefly, comprisesisocyanate which without isolation is treated with an alcohol to givethe corresponding alkyl-3-bromopropionylurethan. Another method ofpreparing the antifoggants of this invention, given in J. Org. Chem, 27,3742 (1962), involves the reaction of oxalyl chloride upon an amide toform an acyl isocyanate which is again treated with an alcohol to formthe corresponding acyl urethan.

at preparation.

EXAMPLE 1 A mixture of 250 ml. of chloroform, 26.7 g. of N-orom'osuecinimide, 1 ml. of allyl chloride, and 5 mg. of oenzoylperoxide was refluxed with stirring for 4 hours. The resulting solutionwas cooled to room temperature, treated with a solution of 28.4 g. ofl-octadecanol in 100 ml. of chloroform and cooled overnight in afreezer. The solid which separated was filtered and dried. Re-:rystallization from ethyl acetate gave 28 g. of colorless :rystals ofoctadecyl-3-bromopropionylurethan having a melting point of 97-98 C.This melting point agrees exactly with that reported in the literature[Johnson et 11., J. Org. Chem, 25, 279, 280 (1960)].

EXAMPLE 2 A mixture of 11.7 g. of 6-bromocaproamide, 7.7 g. of Jxalylchloride, and 140 ml. of 1,2-dichloroethane was refluxed for 6 hours,cooled to room temperature, treated with 2.8 g. of ethanol, and allowedto stand overnight. The solid thus formed was filtered, andrecrystallized once from ligroin and twice from cyclohexane to give 7.5g. )f colorless crystals of ethyl-6-bromocaproylurethan havng a meltingpoint of 78-8l C.

Analysis.Calcd. for C H BrNO z C, 40.6%; H, 3.02%. Found: C, 41.0%; H,6.1%.

The photographic emulsions used in practicing our in- Iention aregenerally of the developing-out type Various silver salts may be used asthe sensitive salt 11 preparing the present emulsions such as silverbromide, :ilver iodide, silver chloride, or mixed silver halides such issilver chlorobromide, silver bromoiodide and the like.

In the preparation 'of the silver halide dispersions emloyed forpreparing silver halide emulsions, there may e employed as thedispersing agent for the silver halide it its preparation, gelatin orsome other hydrophilic coloidal material such as colloidal albumin, acellulose lerivative or a synthetic resin, for instance, a polyvinyl:ompound. Some colloids which may be used are loly(vinyl alcohol) or ahydrolyzed poly(vinyl acetate) lS described in Lowe US. Patent2,286,215, issued June .6, 1942.

The emulsions of the invention can contain convenional photographicsilver halide emulsion addenda such 18 optical sensitizers, chemicalsensitizers, coating aids, gelatin hardeners, plasticizers, and thelike, as well as ither antifoggants in conjunction with the presentantioggants.

The present photographic emulsions of the invention :an be coated on anyof the conventional photographic supports including paper, cellulose,acetate film, poly:

ethylene film, polyethyleneterephthalate film, polystyrene film, glassand the like.

The optimum amount of fog-inhibiting agent can be determined by makingthe customary tests employed in emulsion making. Of course, the optimum,amountfor a given emulsion will vary dependingon the presence ofemulsion addenda, such as chemical 'sensitizers, optical sensitizers,etc. In general we have found that from about .01 to about 20 g. offog-inhibiting agent per mole of silver halide is suitable for thepurpose of our invention, with a preferred range of from about .1,toabout 10 g. of fog-inhibiting agent per mole of silver halide;Instead of adding the fog-inhibiting agent directly to the. photographicemulsion, it is sometimes desirable to.in-" corporate the fog-inhibitingagent in a separate water-. permeable hydrophilic colloid layer which iscontiguous? with the silver halide emulsion layer which is to bestabilized. In such embodiments of the invention we prefer to use thehigherconcentrations of fog-inhibiting agents.

The present invention is further illustrated by the folthe varioustested antifoggants was determined by meas uring the speed, gamma andfog of the incubated emulsions containing an antifoggant and comparingthese measurements with those of the same batch of emulsion beforeincubation. Also, similar measurements were made with a photographicemulsion containing no anti-L The tests foggant both before and afterincubation. were made using high speed, negative-type silverbrom'oiodide emulsions (coated on cellulose acetate supports),

which had been panchromatically sensitized with cyanine.

dyes. The test films were exposed onan intensity scale sensitometer(Kodak Type Ib) and developed for 5 minutes at 68 F. in the followingcomposition:

, I Gms. p-Methylaminophenol sulfate 2.5 Sodium sulfite, desiccated30.0' Hydroquinone v 2.5 Sodium metaborate, octahydrate 10.0

Potassium bromide Water to make 1 liter.

The speed, gamma and fog for each of the emulsioncoatings were thenmeasured as indicated above. The 7 results obtained are given in thefollowing tables.

Table I Com- Cnncen- Fresh Coatings Incubated Coatings Example poundtration,

No. gmslmole AgX Speed Gamma Fog I Speed Gamma Fog Control 160 0. 9O 0.1O 0. 73 0. 28

Table II Fresh Coatings Incubated Coatings Comt-i Concentrai Exam le ountion, gms.

p N mole gX Speed Gamma Fog Speed Gamma Fog II t Br(oH2),,oNHC-oRwherein n is an integer of 1 to 7 and R is an alkyl radical. 3. Aphotographic silver halide emulsion containing an antifoggant compoundhaving the formula:

wherein R is an alkyl radical having 1 to 18 carbon atoms.

4. A photographic gelatino silver halide developing-out emulsioncontaining from about .01 g. to about 20 g. per mole of silver halide ofan antifoggant having the following formula:

Br(oHz)riiNHooGH2-omBr 5. A photographic gelatino silver halidedeveloping-out emulsion containing from about .01 g. to about 20 g. permole of silver halide of an antifoggant having the following formula:

6. A photographic gelatino silver halide developing-out emulsioncontaining from about .01 'g. to about 20 g. per mole of silver halideof an antifoggant having the following formula:

7. A photographic gelatino silver halide developing-out emulsioncontaining from about .01 g. to about 20 g. per

6 mole of silver halide of an antifoggant having the following formula:

Br(CH2)2-%NH%O(CH2)11-CH 9. A photographic gelatino silver halidedeveloping-out emulsion containing from about .01 g. to about 20 g. per

mole of silver halide of an antifoggant having the following formula:

10. A photographic element comprising a photographic silver halideemulsion layer and a contiguous water-permeable hydrophilic colloidlayer, at least one of said layers containing analkyl(monobromoalkanoyl)urethan.

=11. A photographic silver halide emulsion as described in claim 2wherein the silver halide is silver brornoiodide.

12. A photographic silver halide emulsion as described in claim 2wherein the R substituent of the antifoggant compound is a haloalkylradical.

1?. A photographic silver halide emulsion as described in claim 3wherein the R substituent of the antifoggant compound is a bromoalkylradical having 1 to 18 carbon atoms.

References Cited by the Examiner NORMAN G. TORCHIN, Primary Examiner.

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINING AN ALKYL(MONOBROMOALKANOYL)URETHAN ANTIFOGGANT. 